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CSC 427: Data Structures and Algorithm Analysis Fall 2004

CSC 427: Data Structures and Algorithm Analysis Fall 2004. C++ review (or What I Expect You to Know from 221/222) program structure, input, output variables, expressions, functions, parameters control: if, if-else, while, for, recursion predefined classes: string, vector, stack, queue

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CSC 427: Data Structures and Algorithm Analysis Fall 2004

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  1. CSC 427: Data Structures and Algorithm Analysis Fall 2004 • C++ review (or What I Expect You to Know from 221/222) • program structure, input, output • variables, expressions, functions, parameters • control: if, if-else, while, for, recursion • predefined classes: string, vector, stack, queue • searching and sorting, algorithm efficiency (?) • user-defined classes, encapsulation, data hiding • pointers, dynamic memory, linked lists

  2. Program structure and I/O • #include to load libraries • every program must have mainfunction (return type int) • C++ comments use // or /* … */ • can output text using cout and << • // ftoc.cpp • ///////////////////////////////////////////////////// • #include <iostream> • using namespace std; • int main() • { • double tempInFahr; • cout << "Enter the temperature (in Fahrenheit): "; • cin >> tempInFahr; • cout << "You entered " << tempInFahr • << " degrees Fahrenheit." << endl • << "That's equivalent to " • << (5.0/9.0 * (tempInFahr - 32)) • << " degrees Celsius" << endl; • return 0; • } • declare a variable by specifying type, followed by variable name — types include int, double, char, bool, string* — can assign a value to a variable using = — can read a value into a variable using standard input stream cin and >> operator

  3. Strings • // greet.cpp • ///////////////////////////////////////////////////////// • #include <iostream> • #include <string> • using namespace std; • int main() • { • string firstName, lastName; • cout << "Enter your name (first then last): "; • cin >> firstName >> lastName; • cout << "Nice to meet you, " << firstName << " "<< lastName • << ". May I just call you " << firstName • << "?" << endl; • return 0; • } • string type is defined in the library file <string> — note: if you used char* in 221/222, this is MUCH better!!!! — can read and write strings just like any other type — when reading a string value, delimited by whitespace

  4. Expressions • // change.cpp • ///////////////////////////////////////////////////////// • #include <iostream> • using namespace std; • int main() • { • int amount; • cout << "Enter an amount (in cents) to make change: "; • cin >> amount; • int quarters = amount/25; • amount = amount%25; • int dimes = amount/10; • amount = amount%10; • int nickels = amount/5; • amount = amount%5; • int pennies = amount; • cout << "Optimal change:" << endl; • cout << " # of quarters =\t" << quarters << endl; • cout << " # of dimes =\t" << dimes << endl; • cout << " # of nickels =\t" << nickels << endl; • cout << " # of pennies =\t" << pennies << endl; • return 0; • } • C++ provides various operators for constructing expressions + - * / % (+ can be applied to strings to concatenate) • cmath library contains many useful routines pow fabs sqrt floor ceil

  5. Constants & formatted I/O • // pizza.cpp Dave Reed 9/6/01 • // • // This program determines the cost per sq. inch of a pizza. • //////////////////////////////////////////////////////////// • #include <iostream> • #include <iomanip> • using namespace std; • const double PI = 3.14159; • int main() • { • double pizzaDiameter, pizzaCost; • cout << "Enter the diameter of the pizza (in inches): "; • cin >> pizzaDiameter; • cout << "Enter the price of the pizza (in dollars): "; • cin >> pizzaCost; • double pizzaArea = PI*(pizzaDiameter*pizzaDiameter)/4.0; • double costPerSqInch = pizzaCost/pizzaArea; • cout << setiosflags(ios::fixed); • cout << "Total area of the pizza: " • << setprecision(4) << pizzaArea << " square inches." • << endl; • cout << " price per square inch = $" • << setprecision(2) << costPerSqInch << "." << endl; • return 0; • } • constants define values that will not change safer (compiler enforces) easier to manage (global OK) • iomanip library contains routines for formatting output setiosflags setprecision setw

  6. Functions • functions encapsulate computations • define once, call many times • abstract away details in main • parameters in function store values passed in as arguments • params & args match by position • should always document any assumptions, return value • // lowhigh.cpp • //////////////////////////////////////////////// • #include <iostream> • using namespace std; • double FahrToCelsius(double tempInFahr) • // Assumes: tempInFahr is a temperature in Fahrenheit • // Returns: equivalent temperature in Celsius • { • return (5.0/9.0 * (tempInFahr - 32)); • } • int main() • { • double lowTemp, highTemp; • cout << "Enter the forecasted low (in degrees Fahrenheit): "; • cin >> lowTemp; • cout << "Enter the forecasted high (in degrees Fahrenheit): "; • cin >> highTemp; • cout << endl • <<"The forecasted low (in Celsius): " << FahrToCelsius(lowTemp) << endl • <<"The forecasted high (in Celsius): " << FahrToCelsius(highTemp) << endl; • return 0; • }

  7. Functions calling functions can place function prototypes above main, then function definitions in any order after main • // convert.cpp • /////////////////////////////// • #include <iostream> • using namespace std; • double centimetersToInches(double cm); • double metersToFeet(double m); • double kilometersToMiles(double km); • int main() • { • double distanceInKM; • cout << "Enter a distance in kilometers: "; • cin >> distanceInKM; • cout << "That's equivalent to " • << kilometersToMiles(distanceInKM) • << " miles." << endl; • return 0; • } • //////////////////////////////////////////// double centimetersToInches(double cm) // Assumes: cm is a length in centimeters // Returns: equivalent length in inches { return cm/2.54; } double metersToFeet(double m) // Assumes: m is a length in meters // Returns: equivalent length in feet { double cm = 100*m; double in = centimetersToInches(cm); return in/12; } double kilometersToMiles(double km) // Assumes: km is a length in meters // Returns: equivalent length in miles { double m = 1000*km; double ft = metersToFeet(m); return ft/5280; }

  8. value vs. reference parameters • by default, parameters are passed by-value • a copy of the input is stored in the parameter (a local variable) • result: value passed in, no changes are passed out • & implies by-reference • the parameter does not refer to a new piece of memory – it is an alias for the argument • result: changes to the parameter simultaneously change the input void foo(int x) { x = 5; cout << x << endl; } int a = 3; foo(a); cout << a << endl; foo(3); note: input can be any value void foo(int & x) { x = 5; cout << x << endl; } int a = 3; foo(a); cout << a << endl; note: input must be a variable

  9. Advantages of functions • computational abstraction • define & reuse • ignore details simplify repeated tasks • avoids repeated code • can generalize using params can place useful functions in library • reuse using #include • // oldmac.cpp • /////////////////////////////////// • #include <iostream> • #include <string> • using namespace std; • void Verse(string animal, string noise); • int main() • { • Verse("cow", "moo"); • Verse("horse", "neigh"); • Verse("duck", "quack"); • return 0; • } • //////////////////////////////////////////////////////////////// • void Verse(string animal, string noise) • // Assumes: animal is an animal name, and noise is the noise it makes • // Results: displays the corresponding OldMacDonald verse • { • cout << "Old MacDonald had a farm, E-I-E-I-O." << endl; • cout << "And on that farm he had a " << animal << ", E-I-E-I-O." << endl; • cout << "With a " << noise << "-" << noise << " here, and a " • << noise << "-" << noise << " there," << endl; • cout << " here a " << noise << ", there a " << noise << ", everywhere a " • << noise << "-" << noise << "." << endl; • cout << "Old MacDonald had a farm, E-I-E-I-O." << endl << endl; • }

  10. If statements • // change.cpp Dave Reed 9/20/01 • ///////////////////////////////////////////////////////// • #include <iostream> • #include <string> • #include <iomanip> • using namespace std; • void DisplayCoins(int numCoins, string coinType); • int main() • { • // PROMPT USER & ASSIGN VARIABLES AS BEFORE • cout << "Optimal change:" << endl; • DisplayCoins(quarters, "quarters"); • DisplayCoins(dimes, "dimes"); • DisplayCoins(nickels, "nickels"); • DisplayCoins(pennies, "pennies"); • return 0; • } • /////////////////////////////////////////////////////////// • void DisplayCoins(int numCoins, string coinType) • // Assumes: numCoins >= 0, coinType is a type of coin (e.g., nickel) • // Results: displays a message if numCoins > 0 • { • if (numCoins > 0) { • cout << setw(4) << numCoins << " " << coinType << endl; • } • } • if statements provide for conditional execution • simple if specifies code to be executed or not (depending on Boolean condition) comparison operators == != > >= < <= logical connectives && || !

  11. 2-way conditional • #include <iostream> • #include <string> • #include <iomanip> • using namespace std; • void DisplayCoins(int numCoins, string singleCoin, string pluralCoin); • int main() • { • // PROMPT USER & ASSIGN VARIABLES AS BEFORE • cout << "Optimal change:" << endl; • DisplayCoins(quarters, "quarter", "quarters"); • DisplayCoins(dimes, "dime", "dimes"); • DisplayCoins(nickels, "nickel", "nickels"); • DisplayCoins(pennies, "penny", "pennies"); • return 0; • } • /////////////////////////////////////////////////////////// • void DisplayCoins(int numCoins, string singleCoin, string pluralCoin) • // Assumes: numCoins >= 0, singleCoin is the name of a single coin • // (e.g., penny), and pluralCoin is the plural (e.g., pennies) • // Results: displays a message if numCoins > 0 • { • if (numCoins == 1) { • cout << setw(4) << numCoins << " " << singleCoin << endl; • } • else if (numCoins > 1) { • cout << setw(4) << numCoins << " " << pluralCoin << endl; • } • } • if-else allows choice between two options • can cascade if-else’s to produce choose from more than two options

  12. Local vs. global scope • #include <iostream> • #include <cmath> • using namespace std; • double WindChill(double temp, double wind); • int main() • { • double temperature; • cout << "Enter the temperature (in degrees Fahrenheit): "; • cin >> temperature; • if (temperature < -35 || temperature > 45) { • cout << "That temperature is too extreme. " • << "Wind-chill is not defined." << endl; • } • else { • int windSpeed; • cout << "Enter the wind speed (in miles per hour): "; • cin >> windSpeed; • cout << endl << "The wind-chill factor is " • << WindChill(temperature, windSpeed) << endl; • } • return 0; • } • double WindChill(double temp, double wind) • // Assumes: -35 <= temp <= 45, wind >= 0 • // Returns: wind-chill factor given temperature and wind speed • { • if (wind < 4) { • return temp; • } • else { • return 35.74 + 0.6215*temp + • (0.4274*temp – 35.75)*pow(wind, 0.16); • } • } • scope = portion of program where variable is accessible • if declared in function or block { … }, then scope is limited to that function/block (i.e., local) • variables declared outside of functions are accessible to all(i.e.,global) • variables should be as local as possible • global constants are OK

  13. C++ libraries • C++ provides numerous libraries of useful code • cmath functions for manipulating numbers, including: • double fabs(double x); • double sqrt(double x); • double ceil(double x); • double floor(double x); • double pow(double x, double y); int numBits; cin >> numBits; cout << "With " << numBits << "bits, " << "you can represent " << pow(2,numBits) << "patterns."; • cctype functions for testing and manipulating characters, including: • bool isalpha(char ch); • bool islower(char ch); • bool isupper(char ch); • bool isdigit(char ch); • bool isspace(char ch); • char tolower(char ch); • char toupper(char ch); char response; cout << "Do you want to play again? (y/n) "; cin >> response; if (tolower(response) == 'y') { PlayGame(); } else { cout << "Thanks for playing." << endl; }

  14. Abstract data types • an abstract data type (ADT) is a collection of data and the associated operations that can be applied to that data • e.g., a string is a sequence of characters enclosed in quotes with operations: concatenation, determine it length, access a character, access a substring, … • EXAMPLE: the C++ string class in <string> DATA: a sequence of characters (enclosed in quotes) MEMBER FUNCTIONS (METHODS): + >> << // operators for concatenation, input, and output int length(); // returns number of chars in string char at(int index); // returns character at index (first index is 0) string substr(int pos, int len); // returns substring starting at pos of length len int find(string substr); // returns position of first occurrence of substr, // returns constant string::npos if not found int find(char ch); // similarly finds index of character ch . . . call a member function/method using '.', e.g., str.length()

  15. Pig Latin (v. 1) • // piglatin.cpp Dave Reed 9/30/01 • // • // First version of Pig Latin translator. • ///////////////////////////////////////////////////////// • #include <iostream> • #include <string> • using namespace std; • string PigLatin(string word); • int main() • { • string word; • cout << "Enter a word: "; • cin >> word; • cout << "That translates to: " << PigLatin(word) << endl; • return 0; • } • //////////////////////////////////////////////////////////// • string PigLatin(string word) • // Assumes: word is a single word (no spaces) • // Returns: the Pig Latin translation of the word • { • return word.substr(1, word.length()-1) + word.at(0) + "ay"; • } suppose we want to convert a word into Pig Latin • simplest version nix  ixnay pig  igpay latin  atinlay banana  ananabay • here, use length at substr +

  16. Pig Latin (v. 2) need to recognize when starts with vowel apple  appleway isthmus  isthmusway ugly way uses || to look for vowels • string PigLatin(string word) • // Assumes: word is a single word (no spaces) • // Returns: the Pig Latin translation of the word • { • if (IsVowel(word.at(0))) { • return word + "way"; • } • else { • return word.substr(1, word.length()-1) + • word.at(0) + "ay"; • } • } • bool IsVowel(char ch) • // Assumes: ch is a letter • // Returns: true if ch is a vowel ("aeiouAEIOU") • { • ch = tolower(ch); • return (ch == 'a' || ch == 'e' || • ch == 'i' || ch == 'o' || ch =='u'); • } // piglatin.cpp Dave Reed 9/30/01 // // Second version of Pig Latin translator. ////////////////////////////////////////// #include <iostream> #include <string> #include <cctype> using namespace std; string PigLatin(string word); bool IsVowel(char ch); int main() { string word; cout << "Enter a word: "; cin >> word; cout << "That translates to: " << PigLatin(word) << endl; return 0; } //////////////////////////////////////////

  17. Pig Latin (v. 3) • string PigLatin(string word) • // Assumes: word is a single word (no spaces) • // Returns: the Pig Latin translation of the word • { • if (IsVowel(word.at(0))) { • return word + "way"; • } • else { • return word.substr(1, word.length()-1) + • word.at(0) + "ay"; • } • } • bool IsVowel(char ch) • // Assumes: ch is a letter • // Returns: true if ch is a vowel ("aeiouAEIOU") • { • const string VOWELS = "aeiouAEIOU"; • return (VOWELS.find(ch) != string::npos); • } better way uses string search • search for ch in a string of vowels // piglatin.cpp Dave Reed 9/30/01 // // Third version of Pig Latin translator. ////////////////////////////////////////// #include <iostream> #include <string> using namespace std; string PigLatin(string word); bool IsVowel(char ch); int main() { string word; cout << "Enter a word: "; cin >> word; cout << "That translates to: " << PigLatin(word) << endl; return 0; } //////////////////////////////////////////

  18. User-defined classes // Die.cpp bool Die::ourInitialized = false; Die::Die(int sides) { if (!ourInitialized) { ourInitialized = true; // call srand once srand(unsigned(time(0))); // randomize } myRollCount = 0; mySides = sides; } int Die::Roll() { int dieRoll = int(rand()) % mySides + 1; myRollCount++; return dieRoll; } int Die::NumSides() const { return mySides; } int Die::NumRolls() const { return myRollCount; } • similar to string, you can define your own classes (types) in C++ // Die.h #ifndef _DIE_H #define _DIE_H #include <ctime> using namespace std; class Die { public: Die(int sides = 6); int Roll(); int NumSides() const; int NumRolls() const; private: int myRollCount; int mySides; static bool ourInitialized; }; #endif

  19. Using user-defined classes • // rollem.cpp • // • // Simulates rolling two dice • ///////////////////////////////////////// • #include <iostream> • #include "Die.h" • using namespace std; • int main() • { • Die sixSided, eightSided(8); • int sum1 = sixSided.Roll() + sixSided.Roll(); • cout << "Two 6-sided dice: " << sum1 << endl; • int sum2 = sixSided.Roll() + eightSided.Roll(); • cout << "6- and 8-sided dice:" << sum2 << endl; • cout << "The " << sixSided.NumSides() • << "-sided die has been rolled " • << sixSided.NumRolls() << " times." << endl; • return 0; • } • must #include .h file • must add .cpp to project • note: • class constructor has default parameter • Roll method is public • # of sides, # of rolls private, but accessor methods are provided

  20. While loops • provide for conditional repetition • pseudo-code: • ROLL DICE; • DISPLAY RESULTS; • while (DICE ARE DIFFERENT){ • ROLL DICE AGAIN; • DISPLAY RESULTS AGAIN; • } • DISPLAY NUMBER OF ROLLS; • again, Die member functions are useful • // doubles.cpp • // • // Simulates rolling two dice until doubles. • ///////////////////////////////////////////// • #include <iostream> • #include "Die.h" • using namespace std; • int main() • { • Die d1, d2; • int roll1 = d1.Roll(); • int roll2 = d2.Roll(); • cout << "You rolled " << roll1 • << " and " << roll2 << endl; • while (roll1 != roll2) { • roll1 = d1.Roll(); • roll2 = d2.Roll(); • cout << "You rolled " << roll1 • << " and " << roll2 << endl; • } • cout << "It took " << d1.NumRolls() << " rolls." • << endl; • return 0; • }

  21. Priming a loop • can avoid redundancy with a KLUDGE (a quick-and-dirty trick for making code work) • only roll the dice inside the loop • initialize the roll variables so that the loop test succeeds the first time • after the first kludgy time, the loop behaves as before • // doubles.cpp • // • // Simulates rolling two dice until doubles. • ///////////////////////////////////////////// • #include <iostream> • #include "Die.h" • using namespace std; • int main() • { • Die d1, d2; • int roll1 = -1; // KLUDGE: initializes rolls • int roll2 = -2; // so that loop is entered • while (roll1 != roll2) { • roll1 = d1.Roll(); • roll2 = d2.Roll(); • cout << "You rolled " << roll1 • << " and " << roll2 << endl; • } • cout << "It took " << d1.NumRolls() << " rolls." • << endl; • return 0; • }

  22. Counters • counters keep track of number of occurrences of some event • must initialize to zero • increment when event occurs INITIALIZE 7-COUNT TO 0; while (HAVEN'T FINISHED ROLLING) { ROLL DICE; IF ROLLED 7, UPDATE 7-COUNT; } DISPLAY 7-COUNT; arithmetic assignments are handy ++ -- += -= *= • // stats.cpp • // • // Simulates rolling two dice, counts 7's. • ////////////////////////////////////////// • #include <iostream> • #include "Die.h" • using namespace std; • const int NUM_ROLLS = 1000; • int main() • { • Die d1, d2; • int sevenCount = 0; • while (d1.NumRolls() < NUM_ROLLS) { • int roll1 = d1.Roll(); • int roll2 = d2.Roll(); • if (roll1 + roll2 == 7) { • sevenCount = sevenCount + 1; • } • } • cout << "Out of " << NUM_ROLLS << " rolls, " • << sevenCount << " were sevens." << endl; • return 0; • }

  23. While loops vs. for loops use for loop when you know the number of repetitions ahead of time use while loop when the number of repetitions is unpredictable • while loop version: • int numTimes = 0; • while (numTimes < 10) { • cout << "Howdy" << endl; • numTimes++; • } • _____________________________ • int i = 1, sum = 0; • while (i <= 100) { • sum += i; • i++; • } • int i = 0; • while (i < MAX) { • DO SOMETHING; • i++; • } • for (int i = 0; i < MAX; i++) { • DO SOMETHING; • } for loop version: for (int numTimes = 0; numTimes < 10; numTimes++) { cout << "Howdy" << endl; } ___________________________________________________ int sum = 0; for (i = 1; i <= 100; i++) { sum += i; }

  24. Pig Latin (final version) • string PigLatin(string word) • // Assumes: word is a single word (no spaces) • // Returns: the Pig Latin translation of the word • { • int vowelIndex = FindVowel(word); • if (vowelIndex == 0 || vowelIndex == string::npos) { • return word + "way"; • } • else { • return word.substr(vowelIndex, • word.length()-vowelIndex) + • word.substr(0, vowelIndex) + "ay"; • } • } • int FindVowel(string str) • // Assumes: str is a single word (no spaces) • // Returns: the index of the first vowel in str, or • // string::npos if no vowel is found • { • for (int index = 0; index < str.length(); index++) { • if (IsVowel(str.at(index))) { • return index; • } • } • return string::npos; • } #include <iostream> #include <string> using namespace std; string PigLatin(string word); bool IsVowel(char ch); int FindVowel(string str); int main() { string word; cout << "Enter a word: "; cin >> word; cout << "That translates to: " << PigLatin(word) << endl; return 0; } //////////////////////////////// bool IsVowel(char ch) // Assumes: ch is a letter // Returns: true if ch is a vowel ("aeiouAEIOU") { const string VOWELS = "aeiouAEIOU"; return VOWELS.find(ch) != string::npos; }

  25. Vectors (flexible arrays) • the vector class is defined in the <vector> library • can declare size at run-time, can even resize on fly • performs bounds-checking on indexing • parameter passing is normal #include <vector> // loads definition of the vector class using namespace std; vector<int> nums(100); // declares a vector of 100 ints // equiv. to int nums[100]; for (int i = 0; i < 100; i++) { // vector elements are accessible via nums[i] = 0; // an index (same as with arrays) } vector<string> words(10); // declares a vector of 10 strings // equiv. to string words[10]; int numGrades; cout << "How many grades are there? "; cin >> numGrades; vector<double> grades(numGrades); // declares a vector of numGrades // doubles (can't be done with arrays)

  26. Reversing an array vs. Reversing a vector #include <iostream> #include <string> using namespace std; const int MAX_SIZE = 100; int main() { string words[MAX_SIZE]; int numWords = 0; string input; while (numWords < MAX_SIZE && cin >> input) { words[numWords] = input; numWords++; } for (int i = numWords-1; i >= 0; i--) { cout << words[i] << endl; } return 0; } #include <iostream> #include <string> #include <vector> using namespace std; const int INITIAL_SIZE = 10; int main() { vector<string> words(INITIAL_SIZE); int numWords = 0; string input; while (cin >> input) { if (numWords == words.size()) { words.resize(2*words.size()); } words[numWords] = input; numWords++; } for (int i = numWords-1; i >= 0; i--) { cout << words[i] << endl; } return 0; } stops processing when array is full simply resizes vector when full, goes on

  27. Vectors as parameters • unlike arrays, vector parameters behave as any other type void foo(vector<int> nums) void foo(vector<int> & nums) { { nums[0] = 999; nums[0] = 999; } } vector<int> numbers(10); vector<int> numbers(10); foo(numbers); foo(numbers); RESULT: nums is a copy of the vector, RESULT: nums is an alias for the numbers vector no change to numbers[0] simultaneously changes numbers[0] • when passing large objects, alternative to by-value exists void Display(const vector<int> & nums) // & implies reference to { // original vector is passed for (int i = 0; i < nums.size(); i++) { // const ensures no changes made cout << nums[i] << endl; } }

  28. Grade cutoff example void ReadGrades(vector<int> & grades, int & numGrades) // Results: reads grades and stores in vector // numGrades is set to the # of grades { string filename; cout << "Enter the grades file name: "; cin >> filename; ifstream myin; myin.open( filename.c_str() ); while (!myin) { cout << "File not found. Try again: "; cin >> filename; myopen.clear(); myin.open( filename.c_str() ); } numGrades = 0; int grade; while (myin >> grade) { if (numGrades == grades.size()) { grades.resize(2*grades.size()); } grades[numGrades] = grade; numGrades++; } myin.close(); } • #include <iostream> • #include <fstream> • #include <vector> • using namespace std; • const int INITIAL_SIZE = 20; • void ReadGrades(vector<int> & grades, • int & numGrades); • int CountAbove(vector<int> grades, • int numGrades, int cutoff); • int main() • { • vector<int> grades(INITIAL_SIZE); • int numGrades; • ReadGrades(grades, numGrades); • int cutoff; • cout << "Enter the desired grade cutoff: "; • cin >> cutoff; • cout << "There are " • << CountAbove(grades, numGrades, cutoff) • << " grades above " << cutoff << endl; • return 0; • } • //////////////////////////////////////////////

  29. Grade cutoff (using push_back) void ReadGrades(vector<int> & grades) { string filename; cout << "Enter the grades file name: "; cin >> filename; ifstream myin; myin.open( filename.c_str() ); while (!myin) { cout << "File not found. Try again: "; cin >> filename; myin.clear(); myin.open( filename.c_str() ); } int grade; while (myin >> grade) { grades.push_back(grade); } myin.close(); } int CountAbove(const vector<int> & grades, int cutoff) { int numAbove = 0; for(int i = 0; i < grades.size(); i++) { if (grades[i] >= cutoff) { numAbove++; } } return numAbove; } • #include <iostream> • #include <fstream> • #include <vector> • using namespace std; • void ReadGrades(vector<int> & grades); • int CountAbove(vector<int> grades, int cutoff); • int main() • { • vector<int> grades; • ReadGrades(grades); • int cutoff; • cout << "Enter the desired grade cutoff: "; • cin >> cutoff; • cout << "There are " • << CountAbove(grades, cutoff) • << " grades above " << cutoff << endl; • return 0; • } • //////////////////////////////////////////////

  30. Class use • class Card { • public: • Card(); • char GetSuit(); • char GetRank(); • int RankValue(); • void Assign(char r, char s); • private: • char rank; • char suit; • }; • class DeckOfCards { • public: • DeckOfCards(); • void Shuffle(); • Card DrawFromTop(); • void PlaceOnBottom(Card c); • bool IsEmpty(); • private: • vector<Card> cards; • int numCards; • }; given the interface for a class, you should be able to use that class (without caring about implementation details) • DeckOfCards deck; • deck.Shuffle(); • for (int i = 0; i < 5; i++) { • Card c = DrawFromTop(); • cout << c.GetRank() << " " • << c.GetSuit() << endl; • deck.PlaceOnBottom(c); • }

  31. Stacks and queues • a stack is a list where all additions, deletions, accesses occur at one end #include <stack> // C++ provides class in library void push(const TYPE & item); // adds item to top of stack void pop(); // removes item at top of stack TYPE & top() const; // returns item at top of stack bool empty() const; // returns true if stack is empty int size() const; // returns size of stack • a queue is a list where additions occur at one end, deletions and accesses occur at the other end #include <queue> // C++ provides class in library void push(const TYPE & item); // adds item to back of queue void pop(); // removes item from front of queue TYPE & front() const; // returns item at front of queue bool empty() const; // returns true if queue is empty int size() const; // returns size of queue

  32. Pointers • a pointer is nothing more than an address (i.e., an integer) • can declare a pointer to a particular type of value using * int * p; string * q; ??? p ??? q • operations on pointers: • dereference operator: given a pointer to some memory location, can access the value stored there using * • address-of operator: given a memory cell, can get its address (i.e., a pointer to it) using & cout << *p << endl; 4 p p = &x; 7 x

  33. Vectors and dynamic arrays • the underlying data structure of a vector is a dynamically-allocated array template <class Type> class vector { public: vector(int size = 0) { vecLength = size; vecList = new Type[size]; } int size() { return vecLength; } Type & operator[](int index) { return vecList[index]; } // OTHER MEMBER FUNCTIONS private: Type * vecList; int vecLength; }; vector object 5 1 2 3 4 5 MEMBER FUNCTIONS • classes with dynamic data fields should have: • copy constructor: specifies how to make a deep copy of an object (instead of just copying pointers) • destructor: automatically called when the object’s lifetime ends, to reclaim dynamic memory

  34. Node class can define a generic Node class – useful for constructing a linked list ADVANTAGES? • template <class Item> class Node • { • public: • Node<Item>(Item item, Node<Item> * ptr = NULL) • { • value = item; • next = ptr; • } • void setValue(Item item) • { • value = item; • } • void setNext(Node<Item> * ptr) • { • next = ptr; • } • Item getValue() • { • return value; • } • Node<Item> * getNext() • { • return next; • } • private: • Item value; • Node<Item> * next; • }; 4 5 6 list Node<int> * list = new Node<int>(5, NULL); Node<int> * temp = new Node<int>(4, list); list = temp; Node<int> * second = list->getNext(); second->setNext(new Node<int>(6, NULL));

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